Many wireless systems 100, most notably 802.11 wireless local area network (“WLAN”) systems, can operate in both an infrastructure mode and a peer-to-peer mode; in other words, as illustrated in FIG. 1, in an infrastructure mode, the mobile stations 102, 104 communicate with each other through the infrastructure device 106 (e.g., access point, base station, or the like), or the information can be communicated directly from mobile station-to-mobile station. The infrastructure device 106, also provides the connection to the wired LAN, depicted by circle 108, via the Ethernet bridge 110. It should be noted that the coverage area of the infrastructure device 106 is depicted by circle 112. It should be noted that WLANs protocols currently in use, such as variations on 802.11, evolved from the Ethernet wired protocols, where each participating mobile station contends equally for bandwidth resources.
As illustrated in FIG. 2, the partial OSI model 200 comprises the physical (PHY) layer 202 and the medium access control (MAC) layer 204. The PHY layer 202 and MAC layer 204 make up the bottom portion of the OSI model 200. The PHY layer 202 is the interface between the MAC layer 204 and the wireless media, which transmits and receives messages (typical referred to as “data frames” or data packets) over a shared wireless link. In 802.11 WLAN systems, the MAC protocol is the mechanism used to deliver reliable messages (e.g., Media Access Data Units, “MSDU's”) over the wireless link. In order to ensure that the messages in 802.11 are reliably sent over the wireless link, the protocol requires that the MSDU be converted to MAC protocol data unit (“MPDU”), by adding a header and a trailer. Once the messages have been appropriately formatted, the message is then forwarded to the appropriate PHY layer to be sent over the wireless link. Since there are multiple PHY layers capable of communicating with the MAC layer, each PHY layer 202 is structured uniquely based on modulation type, to allow a mobile station to transmit and receive messages at a designated data rate. It should be noted that the MPDU is referred to as a PLCP protocol data unit (“PPDU”) depending on the PHY layer type, however the format and the functions are essentially the same. It should also be noted that the PHY layer 202 is composed of physical layer convergence sublayer (PLCP) 206 and a physical medium dependent sublayer (PMD) 208.
As shown in FIG. 3, the basic format of the PHY layer 300 includes a preamble 314, a PHY header 306, and message depicted by fragment1 308, fragment2 310, and fragment3 312. The preamble consists of a SYNC field 302 and a start of frame delimiter (SFD) field 304. The mobile station uses the SYNC field to capture the incoming signal and to synchronize its receiver and the SFD field to indicate the start of the message. The SYNC field 302 also allows for ramping up and down the transmit power, establishing bit edge determination at the receiver of the mobile station, and an energy measurement interval for antenna diversity. Each preamble 300 is followed by a PHY header 306, the next fragment2 310. The cycle is repeated with Preamble 314, PHY header 306 and, fragment3 312 until the all fragments in the set are received.
In actual practice, many WLANs implementations utilize the infrastructure mode, with all mobiles stations communicating to a wired LAN 108 through the infrastructure device 106. Therefore, the majority of the traffic is “downlink” (e.g., messages flow over the wireless link from the fixed infrastructure device 106 to the mobile stations 102, 104).
A major disadvantage resulting from the manner in which the mobile stations 102, 104 communicate with each other when operating in the infrastructure mode is that the throughput on the air interface in increased, consuming twice the bandwidth.
Another disadvantage is that in applications, such as multimedia voice, individual messages are small such that functions performed by the SYNC field 302 (e.g., establishing bitsync headers and ramp up times, etc.) add significantly to the overhead. This is particularly impactful as the bitsync headers are sent at the slowest, least common denominator data rates available in order to support backward compatibility and derated performance.
Nevertheless, in the infrastructure mode, a mobile station 102, 104 is required to transmit to the infrastructure device 106 within the bounds of the existing protocols. Thus, there exists a need for a method to achieve greater throughput when operating in the infrastructure mode in a WLAN environment.